Pipelines are used to transport oil, gas and the like, e.g. from oil rigs to the shore. Such oil fluid contains constituents of water, and since the pipelines lie on the sea-bed covered by water, the ambient temperature may result in a cooling of the oil fluid to such an extent that the water constituents precipitate as ice on the inside wall of the pipeline. The precipitated ice may, at least partly, block the flow in the pipelines, thus decreasing the velocity of the oil fluid.
Furthermore, casings downhole may, at least partly, be blocked by scales due to the fact that the water constituents in the oil may comprise alkaline earth cations and anions, and water-insoluble scales are formed when cations and anions are present in a certain concentration.
When the precipitated solids, such as ice and scales, are loosened, some solids are of a size making them unable to pass the known releasing tools, causing the tool to get stuck.
Furthermore, when drilling downhole, formation pieces are released from the formation, and such pieces may also be of such size that the pieces are not able to pass the tool.